<div class="cell" :title="cells[c][r]" @click="editing = true">
  <input
    v-if="editing"
    :value="cells[c][r]"
    @change="update"
    @blur="update"
    @vnode-mounted="({ el }) => el.focus()"
  >
  <span v-else>{{ evalCell(cells[c][r]) }}</span>
</div>
